1. Field of the Invention
The present invention relates to a sheet humidification apparatus and a control method thereof for humidifying a sheet on which an image has been formed.
2. Description of Related Art
In electrophotographic image forming apparatuses such as a copier, a printer, a facsimile machine apparatus, and a multifunctional device having such functions, the moisture of the sheet is reduced during a fixation process using heat.
As a result, the dried sheet may be curled or deformed into a wavy shape. In addition to the curl, the sheet may also have static electricity or heat resulting from the fixation processes. Consequently, jam may be easily caused, and the subsequent processes may be negatively influenced.
To solve the above-mentioned problems, a configuration for humidifying the sheet subjected to the fixation process has been proposed. Specifically, for the purpose of removing the curl of the sheet, discharging the sheet, and cooling down the sheet, the sheet is conveyed with moisturized humidification rollers to humidify the sheet. Instead of the configuration using the humidification roller, a method of spraying water vapor to the sheet has also been proposed.
Variations and approaches of such image forming apparatuses are disclosed in Japanese Patent Application Laid-Open No. 2007-292914 and Japanese Patent Application Laid-Open No. 2012-237924.
In Japanese Patent Application Laid-Open No. 2007-292914, the pressure contacting state of the draining roller on the humidification roller is switched in accordance with the condition of each sheet to control the humidification amount. In this case, humidification is appropriately performed in accordance with the upper limit of each sheet to prevent curling and waviness of the sheet, and ensure flatness.
In addition, in Japanese Patent Application Laid-Open No. 2012-237924, whether humidification is performed is switched according to the image formation of each sheet to prevent image defect.
In the above-mentioned manner, by humidifying the sheet output from the thermal fixation apparatus with the sheet humidification device, curling and waviness of the sheet and the like can be reduced and flatness can be ensured.
However, it is found that the sheet winds around the humidification roller under the influence of the water of the humidified sheet surface when the above-mentioned humidification is performed. Likewise, also in the case where the sheet is humidified by water vapor spraying, a situation where a sheet winds around the conveyance roller immediately after the humidification easily occurs.
Such sheet winding is a conveyance failure, and requires the operation of the apparatus to be stopped. In the case where the sheet humidification apparatus is a part of an image formation system, the entire operation of the image formation system has to be stopped, and the productivity disadvantageously decreases.